The present invention relates to the field of keyboard musical instruments, and more particularly to an apparatus and related method for accurately sensing key movement for recording.
Generally musical performances can be recorded either for sound through analog audio recordings, or in a digital format such as Musical Instrument Digital Interface (MIDI) which stores the actual notes including velocities and duration of key movements in digital format. The MIDI standard has been around for several years, and is widely adopted by the music industry.
There are many devices on the market which allow the piano/keyboard to record MIDI output from a performance, most involve the use of photo-interrupters or optical reflective sensors to determine key velocity. A microprocessor (or microcontroller) is used to determine the time it takes for the key to travel between two distances, and translate the time to a given velocity. MIDI can be and is used as the main information to play notes as it can describe 127 different velocities (actually 128 if you include the xe2x80x9cvelocityxe2x80x9d of the note not playing at all), for all the keys on the piano keyboard.
When using MIDI, there are several bytes of information that are transmitted every time a key is pressed or released. Generally, when a key is pressed, three bytes are transmitted including: (1) Note On; (2) Key Number; and (3) Velocity (of that key). Likewise, when a key is released, three additional bytes are transmitted including: (1) Note Off; (2) Key Number; and (3) Velocity (of the key being released).
Unfortunately for pianos and similar instruments, outfitting a keyboard to record key movements can be very difficult in view of the significant amount of wiring and cables required. Unlike electronic keyboards, pianos must have their mechanical action routinely regulated (serviced). This means that the keyboard and the adjoining keybed must be accessible for removal from the piano. If the piano is equipped with a recording device, all connections must be removed prior to removal of the keybed and work on the key action. This causes constant mechanical stress on the cables and connectors, and increases the likelihood that something will fail during or after the servicing process.
This invention substantially eliminates the above noted drawbacks of presently available devices by completely eliminating all mechanical or electronic connections between the keyboard/keybed and the rest of the musical instrument (strings and soundboard). As there is no physical connection between the two parts, the keyboard can be removed and replaced easily to and from the piano with no chance of any wires or cables breaking.
As an added benefit, an algorithm has been developed to allow any deficiency in mounting of the sensors to be corrected mathematically. This is important as not all 88 sensors will be absolutely identically installed on the piano""s 88 keys. This algorithm will correct and adjust the physical variations of the sensor""s mounting inside the piano.
Accordingly, it is a primary object of the present invention to provide a novel and improved apparatus and related method that are particularly adapted to sense key movement and determine velocity in a keyboard musical instrument for recording.
Additional objects, advantages and other novel features of the invention will be set forth in part in the description that follows and in part will become apparent to those skilled in the art upon examination of the following or may be learned with the practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the foregoing and other objects, and in accordance with the purposes of the present invention as described herein, there is provided an improved apparatus capable of sensing a movement and determining a velocity of a key of a keyboard musical instrument for recording. In accordance with the broadest teachings of the present invention, the device and related methods may be applied to digital pianos, electronic keyboards, or other musical devices that are capable of generating sounds by pressing a button or key. However, the description that follows will focus primarily on the invention as it pertains to an acoustic piano.
A standard piano keyboard has 88 keys and three foot pedals. The system described here pertains to recording both the keys and the pedals, though most discussion here will focus on key movement as it is more complex.
Key movement is generally in an up/down (vertical) direction. Total movement is about xc2xd inch (or 12 mm). In this case, movement is determined by use of a small magnet placed on the back end or rear portion of the key (underneath the hammers), and a magnetic sensor is placed across from and facing the magnet, but attached to the piano frame. The magnetic sensor can sense movement by the changing polarity of the magnet mounted on the key as it moves upward or downward. The magnet is preferably xc2xd inch (12 mm) or greater in length so the magnet is always present over the key. The sensor will output a voltage proportional to the polarity of the magnet that is currently directly over the sensor.
Keys can also shift slightly in the horizontal direction. This is especially true in grand pianos, where the xe2x80x9csoft pedalxe2x80x9d will cause a shift of approximately {fraction (3/16)} inch (4 mm) to the side. The soft pedal is used quite often in music, and is necessary to record key movement while the key has shifted to the side. To account for this, the magnet used in this invention preferably has a width of xc2xc inch (6 mm) or greater, so that as the key shifts sideways, the magnet""s position is still over the sensor (not to the side of it).
Magnets and magnetic sensors provide high stability over time, in varying temperature and humidity conditions. AINiCo magnets, for instance, will loose only 3% of their strength in 100,000 hours (11.4 years). Magnetic sensors have almost no change at all over time. Heat and humidity problems for both devices are virtually non-existent. AINiCo magnets, which were used for testing of this invention, will only demagnetize at temperatures over 500 degrees Fahrenheit.
Magnetic sensors in general require much less power than optical sensors. In fact, most magnetic sensors use 70% less power than their optical counterpart. This when multiplied by 88 keys and three pedals makes for a substantial power savings for the entire system. Because of the power savings, the magnetic sensors used in this invention can be left on continuously rather than being pulsed or multiplexed which is often required for optical sensors. By leaving the sensors on continuously, a voltage measurement can be made instantly at any given time, rather than having to wait for the sensor to warm-up.
Because of the unique placement of the magnet on the back side of the keys, and the sensor on the frame of the piano, there is no disconnection of any sort required to remove the piano action (keyboard/keybed) from the piano. The magnets stay with the keys, and the sensors (and associated electronics such as analog to digital converters, microcontrollers, and power supply in the present preferred embodiment) stay with the piano frame. This makes servicing (regulation) of the piano much easier.
Accordingly several advantages are offered by the present invention, including: (1) accuracy of recording is extremely accurate as sensors are unaffected by temperature, humidity or age; (2) sensor to sensor variation in magnetic sensors is much less than optical sensors, so there is much similarity between all 88 key sensors in the system; (3) low power means that sensors can be left on continuously, allowing for instant monitoring of key movements, i.e., no sensor xe2x80x9cwarm-upxe2x80x9d period is required; (4) shifting of the keys in the horizontal direction (soft pedal) has no adverse effect on the recording of key movement; (5) self-calibration is automatic due to an embedded algorithm; (though sensors are highly accurate and reliable, the physical positioning of these sensors may vary slightly due to the person installing the 88 sensors, this algorithm will correct any minor variations); (6) unique mounting of magnets and sensors allows easy servicing of piano action; and (7) no effect on the feel of key as the weight of magnet is extremely small (less than 1%) compared to that of the key""s weighting.
Still other objects of the present invention will become apparent to those skilled in this art from the following description wherein there is shown and described the preferred embodiments of this invention, simply by way of illustration of some of the modes best suited to carry out the invention. As it will be realized, the invention is capable of other different embodiments and its several details are capable of modification in various, obvious aspects all without departing from the invention. Accordingly, the drawings and descriptions will be regarded as illustrative in nature and not as restrictive